In Fig. REF , we compare the performance of various algorithms, which include: 1) General case (`General-Case Alg.'); 2) High-SNR case (`High-SNR Alg.'); 3) Exhaustive search algorithm (`Exhaus. Search'); 4) Fixed location with \(x=(d_1+d_2)/2\)  (`Fixed-Loca.'); 5) Fixed power allocation with \(p_1=p_2=P_T/2\)  (`Fixed-Power'). We also compare the proposed algorithm for AF relay with the one for DF relay in [1]}. For the DF relay, the number of channel uses for the signal processing at the relay is denoted as DD In general, the system bandwidth is fixed, and then the number of channel users can be interpreted as time duration.. It is observed in Fig. REF  that the proposed two algorithms significantly outperform the Fixed-Loca. algorithm and Fixed-Power algorithm, which confirms the benefits of our proposed algorithms. It is interesting to find that the proposed two algorithms have almost the same performance as the exhaustive search method. This may be due to the fact that the SNR in this example generally operates in a very high regime. When the signal processing delay DD is small (e.g. DD=10), the DF relay outperforms the AF relay, which means DF relay is a good option. On the other hand, when DD is large, the AF relay performs better than the DF relay when the number of channel blocklength \(M\)  is small. In this example, when DD=20, the performance of the AF relay is better than that of the DF relay when \(M\le 85\) . This means that it is beneficial to adopt the AF relay when the latency requirement is stringent, which is usually the case in URLLC applications. The reason is that when more time is used for signal processing, the left time for data transmission will be reduced, which decreases the reliability performance.
